1. Field of the Invention
The present invention relates to a wiper control circuit for receiving an operation instruction to a vehicle mounted device.
2. Description of the Related Art
Operation switches for operating equipment such as a wiper and headlights are provided in an automotive vehicle. It often occurs that a user turns an ignition key off to stop an engine and park the automotive vehicle with the operation keys kept on. If the user gets into the automotive vehicle and turns the ignition key on again in such a state, the wiper operates and/or the headlights are turned on according to the operation switches kept on. Particularly, if the ignition key is turned off to park the automotive vehicle on a rainy day with the wiper switch kept on and turned on again on a sunny day to operate the wiper, the rubber of the wiper may be damaged due to friction with a dry windshield or may damage the windshield.
On the other hand, remote control engine starters, with which a user can start an engine by operating operation switches having a wireless communication function at a position remote from an automotive vehicle, are being widely used. In the case of starting the engine using such a remote control engine starter, the user cannot confirm the states of operation switches for a wiper, headlights and the like before starting the engine, wherefore it more often occurs that the wiper operates and/or the headlights are turned on according to the states of the operation switches before parking.
In addition, in the case of starting the engine using the remote control engine starter, the user is often at a position remote from the automotive vehicle. Accordingly, even if the wiper operates and/or the headlights are turned on according to the states of the operation switches before parking, it takes time until the user gets into the automotive vehicle and turns these operation switches off. Thus, time during which the rubber of the wiper rubs the dry windshield as described above becomes longer to further the damage of the wiper rubber and the damage of the windshield. Further, if the headlights are on when the engine is started, an output voltage of a battery decreases, whereby the engine may not be possibly started.
Accordingly, there has been known technology for invalidating the states of operation switches such as a wiper and headlights to suppress unnecessary operations of the wiper and the headlights upon starting an engine using a remote control engine starter as disclosed in Japanese Unexamined Patent Publication No. 2002-266675.
FIG. 2 is a circuit diagram showing a wiper control circuit configured to invalidate the state of a wiper operation switch upon starting an engine using a remote control engine starter. With a wiper control circuit 101 shown in FIG. 2 are connected a battery 201, a combination switch 102 integrally including a wiper operation switch, a remote control engine starter 202 and a relay switch 103. The combination switch 102 includes a variable resistor 105 whose resistance value changes according to an instruction to set an interrupt time for causing the wiper to perform an interrupt operation, a Hi switch 106 for causing a high-speed operation of the wiper, a Lo switch 107 for causing a low-speed operation of the wiper and an INT switch 108 for causing the interrupt operation of the wiper.
A power supply voltage of 12 V is supplied from the battery 201 to the wiper control circuit 101, a control power supply voltage of 5 V supplied from a control power supply circuit 130 is supplied to a ground via a digital transistor 109, a resistor 110, the variable resistor 105 and the relay switch 103. The digital transistor 109 is constructed by integrating a transistor and a resistive element into a circuit, and a diode 111 is connected in a reverse direction between an emitter and a collector of the digital transistor 109.
A base terminal of the digital transistor 109 is connected with the ground via a diode 119 and a digital transistor 118.
The power supply voltage of 12 V supplied from the battery 201 installed in an automotive vehicle is supplied to the ground via a transistor 112, a resistor 113, a diode 114, the operation switch 108 and the relay switch 103. A resistor 115 is connected between an emitter and a base of the transistor 112, and the base of the transistor 112 is connected to the ground via a resistor 116, a diode 117 and the digital transistor 118.
A base terminal of the digital transistor 118 is connected to a signal output terminal OUT of a microcomputer 104. Thus, by outputting a control signal from the microcomputer 104 to turn the digital transistor 118 on, for example, when an ignition key is turned on or an engine is started using the remote control engine starter, the digital transistor 109 and the transistor 112 are turned on to supply the power supply voltages of 5 V and 12 V to the combination switch 102.
A connection node of the variable resistor 105 and the resistor 110 is connected to an analog input terminal AD of the microcomputer 104 via a resistor 120. The microcomputer 104 includes an AD converter so as to be able to convert a voltage inputted to the analog input terminal AD, i.e. a voltage value indicating the interrupt time of the wiper and generated according to the resistance value of the variable resistor 105 into a digital value. A noise removing capacitor 121 is attached to the analog input terminal AD.
An anode of the diode 114 is connected to a base terminal of a digital transistor 125 via a resistor 122. A voltage outputted from a collector terminal of the digital transistor 125 is inputted to a signal input terminal IN of the microcomputer 104 via a resistor 123. The collector terminal of the digital transistor 125 is connected to the ground via a resistor 124.
Thus, ON- and OFF-states of the INT switch 108 are inputted as high and low voltages to the signal input terminal IN to be detectable by the microcomputer 104. Since circuits connected to the Hi switch 106 and the Lo switch 107 are similar to a circuit 148 connected to the INT switch 108, they are not described.
A control terminal of the relay switch 103 is connected to the externally connected remote control engine starter 202. The remote control engine starter 202 is for invalidating the states of the operation switches 106, 107 and 108 to suppress an unnecessary operation of the wiper upon starting the engine by turning the relay switch 103 off.
However, in the wiper control circuit 101 shown in FIG. 2, when the relay switch 103 is turned off by the remote control engine starter 202, the power supply voltage of 12 V supplied from the battery is, for example, supplied to the control power supply circuit of a 5V system having a voltage lower than the battery voltage via the transistor 112, the resistor 113, the diode 114, the operation switch 108 in the ON-state, the variable resistor 105, the resistor 110 and the diode 111. Then, the digital transistor 125 is turned on and the microcomputer 104 recognizes the ON-state of the operation switch 108, resulting in a problem that the wiper and the headlights may be operated contrary to intention.
Further, the power supply voltage of 12 V also sneaks around to the analog input terminal AD of the microcomputer 104 via the transistor 112, the resistor 113, the diode 114, the operation switch 108 in the ON-state, the variable resistor 105 and the resistor 120. In the case where a maximum rated voltage of the analog input terminal AD is 5 V, if a voltage applied to the analog input terminal AD exceeds 5V by sneaking, there has been a problem that a malfunction such as an error in a detected voltage at unillustrated another analog input terminal provided in the microcomputer 104 may occur.